Документ взят из кэша поисковой машины. Адрес оригинального документа :
http://www.naic.edu/~phil/hardware/cor/sbc1_polB_dc_spike_aug11.html
Дата изменения: Mon Aug 15 22:54:37 2011
Дата индексирования: Mon Feb 4 23:21:10 2013
Кодировка:
spike center of band:sbc1 polB jul-aug11
15aug11
A 1 channel wide spike was found in the center of sbc 1, polB using the interim correlator. It did not occur with the 25 Mhz bandwidth.
Properities:
spike in center of the band, 1 channel wide.
Only found in polB
Found in bandwidths 12.5,6.25.. all the way to 195 Khz
It was not found in the 50 or 25 Mhz bands
It was seen in 3 level (and stokes) and 9 level configurations.
It existed:
27jul11 13:00 first appeared
12aug11 13:00 problem went away.
We started to work on the problem
cycled power on halfband filter chassis (problem remained)
removed halfband filter chassis from rack, opened the chassis and started running the program so we could probe things
problem went away.
Projects affected by this:
a2600: 30jul11,31jul11
a2619: 28jul11,31jul11
a2585: 30jul11,31jul11
a2598: 30jul11, 31jul11
The plots show
an example of the problem (.ps)
(
.pdf
):
page 1: spectra (5 sec average)
black 3 level, red 9 level
frame 1,2: 25 Mhz polA,polB
frame 3: 12.5 Mhz polA
frame 4: 12.5 Mhz polB
the spike is 1 channel wide at the center of the band
The spike was seen in all bandwidths below 25Mhz (but no in 25 Mhz)
Page 2: total power tsys versus bandwidth (3 level)
+ symbols polA
* symbols polB
the sbc's are colored
black:sbc1
red: sbc2
green:sbc3
blue:sbc4
The large spike is causing the Tsys to increase.
Page 3: total power tsys vs bandwdith or 9 level
Summary:
A large spike in the center of the band (5 times Tsys) occurred for:
polB sbc1 bandwidths 12.5Mhz and below, 3 and 9 level
it was present 27jul11 13:00 thru 12aug11 13:00
It took so long to find the problem because there was a two week 430 Mhz world day run starting at the beginning of aug11.
The problem disappeared after we opened the halfband filter chassis and reran the program
cycling the power did not make the problem go away
when opening the chassis we had to disconnect and reconnect the cables to the halfband filter chassis.
The operators reported a power dip 27jul11 in the morning.. they may or may not have had something to do with it.
The initial band starts out as 50 Mhz with the a/d dc spike on the left of the band.
As the bandwidths are halved, the a/d dc spike is removed.
A spike in the center of the band has been seen before (sep 2002) but at a much weaker level.
For each bandwidth, the clock for the next narrower bandwidth lies in the center of the band. eg:
for 12.5 Mhz bw, the 6.25 Mhz clock is in the center of the 12.5 Mhz bw
This does not explain why the 25 Mhz bandwidth did not have a spike.. so maybe something else was wrong.
processing: 110812/chkicorrErr.pro
up_to_interim cor page
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